Patrick Dempsey Talks About His Twin Sons

Patrick Dempsey's twin boys are only 10 weeks old, but they already have "distinct personalities," the Grey's Anatomy star says.

"Sullivan is very funny – he has funny expressions in the way he's taking things in – and Darby is very reserved and quiet," Dempsey, 41, told PEOPLE on Saturday, the day before the Grand Am Koni Challenge race in Homestead, Fla., where he was driving for the Hyper Sport team.

And how is his 5-year-old daughter Talula handling the new additions, who were born on Feb. 1?

"Talula is making the transition very well," Dempsey said. "Last week we had father-daughter time – we went and saw Wicked. We'll start doing more one-on-one trips."

Dempsey, who has credited wife Jillian with encouraging him to pursue his dream of racing cars, said he is eager for his children to come to the racetrack with him.

"Talula already wants to drive," he said. "She likes my silver Mercedes with the red interior. I'm glad because it's a sedan so the whole family can ride with her when she learns to drive."

(Dempsey and co-driver Charles Espenlaub finished sixth of 39 cars in the race on Sunday – his best finish in five Koni Challenge races.)